Planar carbon fiber electrode structure

Abstract

Electrodes are disclosed which comprise a porous conductive material as a primary electrode component in electrical contact with a secondary electrode component which preferably is a metal, such as titanium. The secondary electrode component is normally conductive when operating as a cathode, and is capable of alternating between being non-conductive when operating as an anode and becoming conductive again when the electrode is operating as a cathode. Processes for removing metallic species from solution utilizing such electrodes are also disclosed.

What is claimed is: 
     
       1. An electrode comprising a secondary electrode component including a surface comprising a metal selected from the group consisting of titanium, tantalum, tungsten, niobium, hafnium, and alloys thereof, said secondary electrode component including a plurality of holes therethrough so as to permit a flow of electrolyte therethrough, electrical contact means in electrical contact with said secondary electrode component so that outside electrical contact to said electrode is made through said secondary electrode component, a primary electrode component comprising a porous conductive material in electrical contact with said secondary electrode component, whereby said electrode is capable of alternating between acting as a cathode and an anode by said secondary electrode component being conductive when said electrode is acting as a cathode, by becoming non-conductive when said electrode is acting as an anode, and by being capable of converting back to being conductive when said electrode is again acting as a cathode. 
     
     
       2. The electrode of claim 1 wherein said porous conductive material comprises carbon fibers. 
     
     
       3. The electrode of claim 2 wherein said carbon fibers are in the form of a bed or mesh. 
     
     
       4. The electrode of claim 1 or 2 wherein said porous conductive material has a surface area to volume ratio of greater than about 100 cm 2  /cm 3 . 
     
     
       5. The electrode of claim 1 wherein said metal comprises titanium. 
     
     
       6. The electrode of claim 1 wherein said plurality of holes are uniformly spaced apart. 
     
     
       7. The electrode of claim 6 wherein said metal comprises titanium. 
     
     
       8. The electrode of claim 4 wherein at least about 80% of the pores of said porous conductive material are in the range of from about 1 to 100 μm. 
     
     
       9. An electrode usable in connection with an electrolyte, said electrode comprising a primary electrode component comprising a porous conductive material, and a secondary electrode component in electrical contact with said primary electrode component, said secondary electrode component comprising a metal which is normally conductive when said electrode is operating as a cathode, and which is capable of alternating between being non-conductive when said electrode is operating as an anode and again becoming conductive when said electrode is again operating as a cathode. 
     
     
       10. The electrode of claim 9 wherein said porous conductive material has a surface area to volume ratio greater than about 100 cm 2  /cm 3 . 
     
     
       11. The electrode of claim 9 wherein said porous conductive material comprises carbon fibers. 
     
     
       12. The electrode of claim 9 wherein said metal of said secondary electrode component is a metal selected from the group consisting of titanium, tantalum, tungsten, niobium, hafnium, and alloys thereof. 
     
     
       13. The electrode of claim 9 wherein said secondary electrode component includes a plurality of holes therethrough so as to permit the flow of said electrolyte through said primary electrode component. 
     
     
       14. The electrode of claim 13 wherein said plurality of holes are uniformly spaced apart. 
     
     
       15. The electrode of claim 12 wherein said metal of said secondary electrode component comprises titanium. 
     
     
       16. The electrode of claim 9 or 10 wherein at least about 80% of the pores of said porous conductive material are in the range of from about 1 to 100 μm. 
     
     
       17. An electrode usable in connection with an aqueous electrolyte, said electrode comprising a primary electrode component comprising a porous conductive material, and a secondary electrode component in electrical contact with said primary electrical component, said secondary electrode component comprising a conductive material comprising a metal selected from the group consisting of titanium, tantalum, tungsten, niobium, hafnium and alloys thereof which reacts with said electrolyte when acting as an anode to produce a non-conductive compound, said non-conductive compound being produced before a sufficient amount of oxygen is produced at said secondary electrode so as to deleteriously affect said primary electrode, said non-conductive compound being capable of converting back into said conductive material upon said anode being again used as a cathode. 
     
     
       18. The electrode of claim 17 wherein said non-conductive compound comprises an oxide of said conductive material. 
     
     
       19. The electrode of claim 17 wherein said porous conductive material comprises carbon fibers. 
     
     
       20. The electrode of claim 19 wherein said conductive material comprises titanium. 
     
     
       21. The electrode of claim 14 wherein said conductive material includes a plurality of holes therethrough so as to permit the flow of said electrolyte through said primary electrode component. 
     
     
       22. The electrode of claim 21 wherein said plurality of holes are uniformly spaced apart. 
     
     
       23. The electrode of claim 20 wherein said conductive material includes a plurality of holes therethrough so as to permit the flow of said electrolyte through said primary electrode component. 
     
     
       24. The electrode of claim 23 wherein said plurality of holes are uniformly spaced apart. 
     
     
       25. An electrode usable in connection with an aqueous electrolyte, said electrode comprising a primary electrode component comprising a porous conductive material, a secondary electrode component in electrical contact with said primary electrode component, and electrical contact means in electrical contact with said secondary electrode component so that outside electrical contact to said electrode is made through said secondary electrode component, said secondary electrode component comprising a conductive material which reacts with said electrolyte when acting as an anode to produce a non-conductive compound, said non-conductive compound being produced before a sufficient amount of a corrosive agent is produced so as to deleteriously affect said primary electrode component, said non-conductive compound also being capable of converting back into said conductive material upon said anode again being used as a cathode. 
     
     
       26. The electrode of claim 1 including flow means for flowing said electrolyte through said electrode when said electrode is acting as a cathode, polarity reversal means for reversing the polarity of said electrode so that it acts as an anode, and sensing means for sensing when said secondary electrode component becomes non-conductive. 
     
     
       27. The electrode of claim 26 including flow sensing means for sensing a reduction in said flow of said electrolyte through said electrode whereby said polarity reversal means may then be actuated. 
     
     
       28. The electrode of claim 27 wherein said flow sensing means comprises a transducer. 
     
     
       29. The electrode of claim 26 or 27 wherein said flow means comprises pump means. 
     
     
       30. The electrode of claim 26 or 27 wherein said sensing means comprises means for sensing a decrease in the current flowing through said electrode. 
     
     
       31. The electrode of claim 26 or 27 wherein said sensing means comprises means for sensing an increase in the voltage across said electrode. 
     
     
       32. The electrode of claim 26 wherein said reverse flow means comprises means for flowing a stripping electrolyte through said electrode.